DRAM cell capacitor having increased trench capacitance

ABSTRACT

A trench capacitor having an increased surface area. In one embodiment, the trench capacitor is a dual trench capacitor having a first trench and a second trench wherein inner walls of the trenches electrically connect. The invention also includes a single trench capacitor wherein the trench is curved around an axis substantially perpendicular to a substrate surface.

TECHNICAL FIELD

The present invention relates generally to a capacitor of a DRAM deviceand, more specifically, to a capacitor of a DRAM device having anincreased surface area and to a process of manufacture.

BACKGROUND OF THE INVENTION

Typical Dynamic Random Access Memory (DRAM) cells have a transferdevice, such as a field effect transistor (FET), having a capacitor forstoring charge. Conventional capacitors include the stacked capacitorand the trench capacitor. In the trench capacitor, charge is storedvertically in a trench extending from a substrate.

The DRAM cell is so named because it can retain information onlytemporarily, on the order of milliseconds, even with power continuouslyapplied. Therefore, the cell must be read and refreshed at periodicintervals. Although the storage time may at first appear very short, itis actually long enough to permit many memory operations between refreshcycles. The advantages of cost per bit, device density, and flexibilityof use (i.e., both read and write operations are possible) have madeDRAM cells the most widely used form of semiconductor memory to date.

Generally, the integrated circuit technology of a DRAM cell is based onthe ability to form numerous transfer devices in a substrate. Recently,new techniques have enabled the reduction of DRAM cell dimensions, suchas by shortening the length of the channel of the FET. As a result, thenumber of integrated circuits fabricated on a wafer has dramaticallyincreased.

Unfortunately, DRAM device shrinkage has also reduced the size of thetrench capacitors of DRAM cells. The reduction of trench capacitorsurface area is the result of numerous factors. One cause of the surfacearea decrease is the reduction in trench mask opening size. A secondcause of surface area decrease in the trench capacitor is the reducedtrench depth that can be attained with the smaller trench mask openingsize. As trench capacitor surface areas shrink, the capacitance of thetrench capacitor also decreases. In addition, trench capacitor leakagedoes not decrease proportionally with capacitor size.

The decrease in the capacitance of conventional capacitors of DRAM cellsshow that a need exists for increasing the capacitance of the trenchcapacitor. To overcome the shortcomings of conventional DRAM cellcapacitors, a new capacitor for a DRAM device and a process forfabricating such a capacitor are provided. An object of the presentinvention is to provide a capacitor of a DRAM device having an increasedcapacitance. A related object is top provide a DRAM capacitor having anincreased capacitor retention time. Still another object of the presentinvention is to provide a process suitable for manufacturing a capacitorof a DRAM device having an increased capacitance and, therefore, anincreased capacitor retention time.

SUMMARY OF THE INVENTION

To achieve these and other objects, and in view of its purposes, thepresent invention provides a capacitor of a DRAM device having anincreased capacitance. Also provided is a process of fabricating thecapacitor. More specifically, the present invention provides a dualtrench capacitor comprising a first trench adjacent a second trench in asubstrate. The trenches have a top on the surface of the substrate, abottom in the substrate, and opposing inner and outer side wallsextending from the top to the bottom. The inner side wall of the firsttrench electrically contacts the inner side wall of the second trench.

The dual trench capacitor of the invention is fabricated by forming amask on a substrate, the mask having a mask island formed betweenopenings in the mask which extend to the surface of the substrate. Thesubstrate is etched through the openings to form the trenches. In oneembodiment, the mask island and a portion of the substrate surfaceunderlying the mask island are removed such that the first trenchelectrically contacts the second trench. In another embodiment, thetrench side walls are radially expanded below a surface of the substratesuch that the trench inner walls electrically contact.

The present invention also provides a trench capacitor having a singletrench, in which the trench is curved around an axis substantiallyperpendicular to the substrate surface. The single trench capacitor ofthe present invention is fabricated by forming a mask on a substrate,the mask having a mask island and an opening curved around an axissubstantially perpendicular to a surface of the substrate. The exposedsubstrate surface is etched to form the trench.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1A shows in schematic representation a first embodiment of a dualtrench capacitor formed in accordance with the present invention;

FIG. 1B shows in schematic representation a top view of the dual trenchcapacitor shown in FIG. 1A;

FIG. 1C shows in schematic representation a top view of the dual trenchcapacitor shown in FIG. 1A, in which trenches curve around an axissubstantially perpendicular to a substrate surface;

FIG. 2 shows in schematic representation a second embodiment of a dualtrench capacitor formed in accordance with the present invention;

FIG. 3A shows in schematic representation a third embodiment of a dualtrench capacitor formed in accordance with the present invention;

FIG. 3B shows in schematic representation a top view of the dual trenchcapacitor shown in FIG. 3A;

FIG. 3C shows in schematic representation a top view of the dual trenchcapacitor shown in FIG. 3A, in which the trenches curve around an axissubstantially perpendicular to a substrate surface;

FIG. 4A shows in schematic representation a fourth embodiment of a dualtrench capacitor formed in accordance with the present invention;

FIG. 4B shows in schematic representation a top view of the dual trenchcapacitor shown in FIG. 4A;

FIG. 4C shows in schematic representation a top view of the dual trenchcapacitor shown in FIG. 4A, in which the trenches curve around an axissubstantially perpendicular to the substrate surface;

FIG. 5 shows in schematic representation a substrate having a maskapplied to the substrate;

FIG. 6 shows in schematic representation the substrate shown in FIG. 5having two trenches formed in the substrate;

FIG. 7 shows in schematic representation a substrate having alternativedual trenches and a mask formed on the substrate;

FIG. 8 shows in schematic representation a substrate having alternativedual trenches and a mask formed on the substrate;

FIG. 9 shows in schematic representation a substrate having stillalternative dual trenches and a mask formed on the substrate;

FIG. 10A shows in schematic representation a single trench capacitorformed in accordance with the present invention;

FIG. 10B shows in schematic representation a top view of the trenchcapacitor shown in FIG. 10A;

FIG. 10C shows in schematic representation a top view of the trenchcapacitor shown in FIG. 10A, in which a trench curves completely aroundan axis substantially perpendicular to a substrate surface;

FIG. 11 shows in schematic representation a single trench capacitorformed in accordance with the present invention;

FIG. 12 shows in schematic representation another single trenchcapacitor formed in accordance with the present invention;

FIG. 13 shows in schematic representation still another single trenchcapacitor formed in accordance with the present invention;

FIG. 14 shows in schematic representation yet a further single trenchcapacitor formed in accordance with the present invention;

FIG. 15 shows in schematic representation a substrate having a maskapplied to the substrate;

FIG. 16 shows in schematic representation a top view of the trenchcapacitor shown in FIG. 15;

FIG. 17 shows in schematic representation a top view of the trenchcapacitor shown in FIG. 15, in which a trench curves completely aroundan axis substantially perpendicular to a substrate surface; and

FIG. 18 shows in schematic representation the substrate shown in FIG. 15having a trench formed in the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will next be described with reference to thefigures in which similar numbers indicate the same elements in allfigures. Such figures are intended to be illustrative, rather thanlimiting, and are included to facilitate the explanation of theapparatus and process of the present invention. It has been discoveredthat, by increasing the surface area of the trench of a trenchcapacitor, the capacitance of the trench increases. The presentinvention relates both to dual trench and single trench capacitors andto a process of fabricating such capacitors.

A. Dual Trench Capacitor

FIGS. 1A through 4C illustrate dual trench capacitors formed inaccordance with the principles of the present invention. It has beendiscovered that when two adjacent trenches are electrically contacted toform a single capacitor, the capacitance of the capacitor increases dueto an increase in the surface area of the capacitor.

FIG. 1A illustrates a first embodiment of the present invention. Asshown in this figure, a substrate 10 is provided. Two trenches 20 areformed in substrate 10. Trenches 20 extend into substrate 10 from asurface 11 of substrate 10.

The trench capacitor illustrated in FIG. 1A is a dual trench capacitor.The inner side walls 21 of trenches 20 are electrically connectedthrough a contact bridge 24 adjacent to surface 11 of substrate 10. Byconnecting two adjacent trenches 20 just below surface 11 of substrate10 by forming contact bridge 24, a trench capacitor having an increasedcapacitance is formed.

Substrate 10 of the present invention can be any material commonly usedas substrates for trench capacitors, such as silicon. During furtherprocessing of the dual trench capacitors of the present invention, suchas the capacitor illustrated in FIG. 1A, a dielectric layer 40 is formedon trench inner side walls 21 and trench outer side walls 22. Dielectriclayer 40 can be selected from those conventionally used, such as siliconoxide, silicon nitride, or combinations of those materials. In addition,a first electrode 50, such as highly doped polysilicon, is deposited intrenches 20 to complete the capacitor. Substrate 10 constitutes a secondelectrode.

FIG. 1B illustrates a top view of the trench capacitor illustrated inFIG. 1A. As shown in FIG. 1B, trenches 20 have an elliptical top viewshape. FIG. 1C illustrates another top view of the trench capacitorillustrated in FIG. 1A. In this embodiment, trenches 20 are curvedaround an axis, A, substantially perpendicular to surface 11 ofsubstrate 10. By forming trenches 20 having this configuration, thesurface area of trenches 20 is further increased, resulting in anadditional increase in the capacitance of the trench capacitor.Therefore, in a preferred embodiment of the present invention, trenches20 are curved around an axis substantially perpendicular to the surface11 of substrate 10, as illustrated in FIG. 1C.

In accordance with the principles of the present invention, the trenchcapacitor illustrated in FIG. 1A is formed by the following steps. Amask 30 is formed on substrate 10. Mask 30 has openings 31 correspondingto regions in where trenches 20 will be formed. This structure isillustrated in FIG. 5. Mask 30 can be any of those masks conventionallyused to form trenches. Mask 30 illustrated in FIG. 5 consists of a firstsilicon oxide layer 32, a nitride layer 33, and a second silicon oxidelayer 34. Substrate 10 can be any of those materials conventionally usedas substrates in DRAM cells, such as silicon.

Following formation of mask 30 on substrate 10, trenches 20 are etchedinto substrate 10. Trenches 20 extend from surface 11 of substrate 10.This structure is illustrated in FIG. 6. Trenches 20 can be formed insubstrate 10 using techniques commonly used to form trenches, such asreactive ion etching (RIE).

When etching trenches 20, the portion of mask 30 between trenches20—referred to as the mask island 35—is often partially eroded, as shownin FIG. 6. It has been discovered that mask island 35 can be completelyeroded such that trenches 20 electrically contact through contact bridge24 adjacent to surface 11 of substrate 10, as illustrated in FIG. 1A.After further processing of trenches 20, the resulting contact bridge 24is composed of a first electrode material. FIG. 7 illustrates thestructure of FIG. 6 after mask island 35 has been eroded.

FIG. 2 illustrates a second embodiment of a dual trench capacitor formedin accordance with the present invention. In comparison to the capacitorof FIG. 1A, the trench inner side walls 21 and outer side walls 22 havebeen radially expanded in the capacitor of FIG. 2. The opposing sidewalls 21, 22 of trenches 20 have been formed such that they curve awayfrom each other from the top of trenches 20 to the bottom. Asillustrated, trenches 20 have an elliptical cross section. Although bothtrenches 20 have been radially expanded in FIG. 2, it may be desirableto radially expand only one of the two trenches.

Radially expanded inner and outer side walls 21, 22, as illustrated inFIG. 2, can be formed using several techniques. When reactive ionetching substrate 10 through mask 30 to form trenches 20, side walls 21,22 can be radially expanded by increasing the cathode temperature of theetching chamber. Side walls 21, 22 can also be radially expanded byetching trench side walls 21, 22 with a plasma comprising NF₃, HBr, andHeO₂. Similarly, side walls 21, 22 can be radially expanded by etchingside walls 21, 22 with a gas selected from SF₆, CF₄, Cl₂, orcombinations of such components. FIG. 8 illustrates a structure in whichside walls 21, 22 have been radially expanded by one of these processes.

FIG. 3A illustrates a third embodiment of the present invention. Asillustrated, two trenches 20 extend from surface 11 of substrate 10. Thedual trench capacitor illustrated in FIG. 3A has trench inner side walls21 that physically contact below surface 11 of substrate 10. Byconnecting two adjacent trenches 20, a dual trench capacitor having anincreased capacitance is formed.

Inner and outer side walls 21, 22 illustrated in FIG. 3A can be radiallyexpanded by increasing the cathode temperature of the etching chamberwhile reactive ion etching trenches 20. Side walls 21, 22 can also beradially expanded by etching trench side walls 21, 22 with a plasmacomprising NF₃, HBr, and HeO₂. Similarly, side walls 21, 22 can beradially expanded using a gas selected from SF₆, CF₄, Cl₂, orcombinations of such components. FIG. 9 illustrates a structure in whichside walls 21, 22 have been radially expanded and physically contactedso that adjacent trenches 20 connect near their midpoints.

FIG. 3B illustrates a top view of the trench capacitor illustrated inFIG. 3A. As shown in FIG. 3B, trenches 20 have an elliptical top viewshape. FIG. 3C illustrates another top view of the trench capacitorillustrated in FIG. 3A. In this embodiment, trenches 20 are curvedaround an axis, B, substantially perpendicular to surface 11 ofsubstrate 10. By forming trenches 20 having this configuration, thesurface area of trenches 20 is further increased, resulting in anadditional increase in the capacitance of the trench capacitor.Therefore, in a preferred embodiment of the present invention, trenches20 are curved around an axis substantially perpendicular to the surface11 of substrate 10, as illustrated in FIG. 3C.

FIG. 4A illustrates a fourth embodiment of the present invention. Asillustrated, two trenches 20 extend from surface 11 of substrate 10. Thedual trench capacitor illustrated in FIG. 4A has the combined featuresof the embodiments of FIGS. 1A and 3A. Specifically, the inner sidewalls 21 of trenches 20 are electrically connected through contactbridge 24 adjacent to surface 11 of substrate 10 and inner side walls 21physically contact below surface 11 of substrate 10. By connecting twoadjacent trenches 20, the dual trench capacitor has an increasedcapacitance.

FIG. 4B illustrates a top view of the trench capacitor illustrated inFIG. 4A. As shown in FIG. 4B, trenches 20 have an elliptical top viewshape. FIG. 4C illustrates another top view of the trench capacitorillustrated in FIG. 4A. In this embodiment, trenches 20 are curvedaround an axis, C, substantially perpendicular to surface 11 ofsubstrate 10. By forming trenches 20 having this configuration, thesurface area of trenches 20 is further increased, resulting in anadditional increase in the capacitance of the trench capacitor.Therefore, in a preferred embodiment of the present invention, trenches20 are curved around an axis substantially perpendicular to the surface11 of substrate 10, as illustrated in FIG. 4C.

B. Single Trench Capacitor

FIGS. 10A through 14 illustrate single trench capacitors formed inaccordance with principles of the present invention. As shown in thesefigures, the trenches of the present invention have an increased surfacearea as compared to conventional trench capacitors. By increasing thesurface area of the trench, the capacitance of the trench capacitor islikewise increased.

FIG. 10A illustrates another embodiment of the present invention. Asshown in this figure, a substrate 10 has a trench 20 formed extendingfrom a surface 11 of substrate 10. The trench capacitor illustrated inFIG. 10A is a single trench capacitor. The single trench capacitor ofthe present invention is formed such that it is curved partially aroundan axis, D, substantially perpendicular to surface 11 of substrate 10.This structure is illustrated, as a top view, in FIG. 10B.

The single trench capacitor can also be formed such that trench 20completely surrounds a mask island 35. Trench 20 completely surroundsand is symmetrical about axis D which is substantially perpendicular tosurface 11 of substrate 10. Thus, trench 20 forms a donut shape as itsurrounds mask island 35. Such a structure is illustrated in FIG. 10C.

By forming trench 20 having these configurations, the surface area oftrench 20 is further increased. Such increases surface area results inan additional increase in the capacitance of the trench capacitor.Therefore, in a preferred embodiment of the present invention, trench 20is curved around an axis substantially perpendicular to the surface 11of substrate 10, as illustrated in FIGS. 10B and 10C.

Substrate 10 of the present invention can be any of those materials usedas substrates for trench capacitors, such as silicon. During furtherprocessing of the single trench capacitors of the present invention,such as the capacitor illustrated in FIG. 10A, a dielectric layer 40 isformed on the trench side walls 21 and 22. Dielectric layer 40 can beselected from those conventionally used, such as silicon oxide, siliconnitride, or combinations of those materials. In addition, a firstelectrode 50, such as highly doped polysilicon, is deposited in trench20 to complete the capacitor.

In accordance with the principles of the present invention, the trenchcapacitor illustrated in FIGS. 10A, 10B, and 10C can be formed by thefollowing steps. A mask 30 is formed on substrate 10. Mask 30 has anopening 31 corresponding to regions in which trench 20 will be formed.This structure is illustrated in FIG. 15. Opening 31 is curved around anaxis substantially perpendicular to the substrate surface, and exposesthe substrate surface.

Next, the exposed substrate surface is etched, thereby forming trench20. Mask 30 can be any of those masks conventionally used to formtrenches. The mask illustrated in FIG. 15 comprises a first siliconoxide layer 32, a nitride layer 33, and a second silicon oxide layer 34.Substrate 10 can be any of those materials conventionally used assubstrates in DRAM cells, such as silicon.

FIGS. 16 and 17 illustrate top views of the single trench capacitorformed in accordance with principles of the present invention. Trench 20illustrated in FIG. 16 is curved partially around an axis substantiallyperpendicular to the substrate surface. Trench 20 illustrated in FIG. 17is curved completely around an axis substantially perpendicular to thesubstrate surface such that it completely surrounds mask island 35.

Following formation of mask 30 on substrate 10, trench 20 is etched intosubstrate 10 extending from surface 11 of substrate 10. This structureis illustrated in FIG. 18. Trench 20 can be formed in substrate 10 usingtechniques conventionally used to form trenches, such as reactive ionetching.

In forming trench 20, mask island 35 between inner side walls 21 oftrench 20 is often partially eroded. It has been discovered that maskisland 35 can be completely eroded such that contact bridge 24 is formedadjacent to surface 11 of substrate 10, as illustrated in FIG. 11.

FIG. 12 illustrates another embodiment of the present invention. Asshown in this figure, trench inner side walls 21 and outer side walls 22have been radially expanded. The opposing side walls 21, 22 of trench 20have been formed such that they curve away from each other from the topof trench 20 to the bottom. As shown in FIG. 12, opposing side walls 21,22 curve in opposite directions and reach a maximum distance from eachother at a point intermediate the top and bottom of trench 20.

The radially expanded side walls 21 and 22, as illustrated in FIG. 12,can be formed using several techniques. When reactive ion etchingsubstrate 10 through mask 30 to form trench 20, side walls 21, 22 can beradially expanded by increasing the cathode temperature of the etchingchamber. Side walls 21, 22 can also be radially expanded by etchingtrench side walls 21, 22 with a plasma comprising NF₃, HBr, and HeO₂.Similarly, side walls 21, 22 can be radially expanded by etching sidewalls 21, 22 with a gas selected from SF₆, CF₄, Cl₂, or combinations ofthose components.

FIG. 13 illustrates another embodiment of the present invention. Asshown in this figure, trench inner side walls 21 and outer side walls 22have been radially expanded such that inner side walls 21 of trench 20physically contact below surface 11 of substrate 10. The single trenchillustrated in FIG. 13 is formed such that it curves partially around anaxis substantially perpendicular to the substrate surface, asillustrated in FIG. 10B.

The trench capacitor illustrated in FIG. 14 is a single trench capacitorhaving the combined features of FIGS. 11 and 13. Specifically, innerside walls 21 of trench 20 are electrically connected through contactbridge 24 adjacent to surface 11 of substrate 10. Inner side walls 21physically contact below surface 11 of substrate 10. The single trenchillustrated in FIG. 14 is formed such that it curves partially around anaxis substantially perpendicular to the substrate surface, asillustrated in FIG. 10B.

Although illustrated and described above with reference to specificembodiments, the present invention is nevertheless not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the spirit of the invention.

What is claimed:
 1. A trench capacitor comprising a first trenchadjacent a second trench in a substrate, said substrate having asurface, each of said trenches having a top on said surface, a bottom insaid substrate, and opposing inner and outer side walls extending fromsaid top to said bottom, wherein the inner wall of said first trenchelectrically contacts the inner wall of said second trench, and whereinthe inner wall of said first trench physically contacts the inner wallof said second trench.
 2. The trench capacitor of claim 1 wherein thesubstrate is silicon.
 3. The trench capacitor of claim 1 wherein saidtrenches have a dielectric layer on the trench side walls and anelectrode deposited in said trenches.
 4. The trench capacitor of claim 3wherein said dielectric layer is silicon oxide.
 5. The trench capacitorof claim 3 wherein said dielectric layer comprises a first silicon oxidelayer, a silicon nitride layer, and a second silicon oxide layer.
 6. Thetrench capacitor of claim 3 wherein said electrode is heavily dopedpolysilicon.
 7. A trench capacitor comprising a first trench adjacent asecond trench in a substrate, said substrate having a surface, each ofsaid trenches having a top on said surface, a bottom in said substrate,and opposing inner and outer side walls extending from said top to saidbottom, wherein the inner wall of said first trench electricallycontacts the inner wall of said second trench, and wherein said opposingside walls in at least one of said trenches curve away from each otherfrom top to bottom.
 8. The trench capacitor of claim 7 wherein thesubstrate is silicon.
 9. The trench capacitor of claim 7 wherein saidtrenches have a dielectric layer on the trench side walls and anelectrode deposited in said trenches.
 10. The trench capacitor of claim9 wherein said dielectric layer is silicon oxide.
 11. The trenchcapacitor of claim 9 wherein said dielectric layer comprises a firstsilicon oxide layer, a silicon nitride layer, and a second silicon oxidelayer.
 12. The trench capacitor of claim 9 wherein said electrode isheavily doped polysilicon.
 13. A trench capacitor comprising a firsttrench adjacent a second trench in a substrate, said substrate having asurface, each of said trenches having a top on said surface, a bottom insaid substrate, and opposing inner and outer side walls extending fromsaid top to said bottom, wherein the inner wall of said first trenchelectrically contacts the inner wall of said second trench, and whereinsaid opposing side walls in at least one of said trenches curve inopposite directions and reach a maximum distance from each other at apoint intermediate the top and bottom of said trench.
 14. The trenchcapacitor of claim 13 wherein the substrate is silicon.
 15. The trenchcapacitor of claim 13 wherein said trenches have a dielectric layer onthe trench side walls and an electrode deposited in said trenches. 16.The trench capacitor of claim 15 wherein said dielectric layer issilicon oxide.
 17. The trench capacitor of claim 15 wherein saiddielectric layer comprises a first silicon oxide layer, a siliconnitride layer, and a second silicon oxide layer.
 18. The trenchcapacitor of claim 15 wherein said electrode is heavily dopedpolysilicon.
 19. A trench capacitor comprising a first trench adjacent asecond trench in a substrate, said substrate having a surface, each ofsaid trenches having a top on said surface, a bottom in said substrate,and opposing inner and outer side walls extending from said top to saidbottom, wherein the inner wall of said first trench electricallycontacts the inner wall of said second trench, and wherein at least oneof said trenches is curved around an axis substantially perpendicular tothe substrate surface.
 20. The trench capacitor of claim 19 wherein thesubstrate is silicon.
 21. The trench capacitor of claim 19 wherein saidtrenches have a dielectric layer on the trench side walls and anelectrode deposited in said trenches.
 22. The trench capacitor of claim21 wherein said dielectric layer is silicon oxide.
 23. The trenchcapacitor of claim 21 wherein said dielectric layer comprises a firstsilicon oxide layer, a silicon nitride layer, and a second silicon oxidelayer.
 24. The trench capacitor of claim 21 wherein said electrode isheavily doped polysilicon.
 25. A trench capacitor comprising a trench ina substrate, said substrate having a surface, wherein the trench iscurved around an axis substantially perpendicular to the substratesurface, said trench having a top on said surface, a bottom in saidsubstrate and opposing inner and outer side walls extending from saidtop to said bottom, curving in opposite directions, and reaching amaximum distance from each other at a point intermediate the top andbottom of said trench.
 26. The trench capacitor of claim 25 wherein saidcurved trench completely surrounds said axis.
 27. The trench capacitorof claim 25 wherein the substrate is silicon.
 28. The trench capacitorof claim 25 wherein the trench has a dielectric layer on the trench sidewalls and an electrode deposited in said trench.
 29. The capacitor ofclaim 28 wherein said dielectric layer is silicon oxide.
 30. Thecapacitor of claim 28 wherein said dielectric layer comprises a firstsilicon oxide layer, a silicon nitride layer, and a second silicon oxidelayer.
 31. The capacitor of claim 28 wherein said electrode is heavilydoped polysilicon.
 32. A trench capacitor comprising a trench in asubstrate, said substrate having a surface, wherein the trench is curvedaround an axis substantially perpendicular to the substrate surface,said trench having a top on said surface, a bottom in said substrate andopposing inner and outer side walls extending from said top to saidbottom with said inner side walls physically contacting.
 33. The trenchcapacitor of claim 32 wherein said curved trench completely surroundssaid axis.
 34. The trench capacitor of claim 32 wherein the substrate issilicon.
 35. The trench capacitor of claim 32 wherein the trench has adielectric layer on the trench side walls and an electrode deposited insaid trench.
 36. The capacitor of claim 35 wherein said dielectric layeris silicon oxide.
 37. The capacitor of claim 35 wherein said dielectriclayer comprises a first silicon oxide layer, a silicon nitride layer,and a second silicon oxide layer.
 38. The capacitor of claim 35 whereinsaid electrode is heavily doped polysilicon.